This looks interesting. The website says legal in all 50 states. For those of you old enough there was something similar to this many years ago except it was powered by Freon gas in cans. Can only do short bursts though because everything would freeze up.
I remember the full auto BB Tommy Guns at the fair every year. They ran on CO2 I believe. They had a hose running down from the pistol grip. You had to shoot the red star out of the paper to win the prize.